Retractable assemblies are widely used in analytical measurements technology. They serve to introduce probes into a process, and, therewith, into a medium, and then to withdraw such from the process, without interrupting the process as it is running, at pressures up to 10 bar and more. The probes are moved by means of a drive manually or automatically, for example, pneumatically, axially between a process position and a service position. In the service position, the probe is typically sealed from the medium.
Probes in the sense of this invention include probes with at least one accommodation for at least one sensor for measuring one or more process variables as well as sample takers, which withdraw from or feed to the process a determined amount of medium.
The fields of use of retractable assemblies for measuring physical or chemical process variables of a medium, e.g. of a fluid, especially a liquid, in process technology are vast. For determining process variables, sensors are used, wherein such sensors include, for example, pH-sensors, conductivity sensors, optical or electrochemical sensors for determining a concentration of a substance contained in the medium to be monitored, e.g. O2, CO2, certain types of ions, organic compounds, etc.
If the retractable assemblies are used for accommodating a sensor for determining at least one process variable, the sensor in the service position can be checked, calibrated, cleaned and/or replaced, wherein the sensor, in such case, is located in a treatment chamber arranged in the housing of the retractable assembly.
If the retractable assemblies are used as sample takers, in the service position, the medium taken by the sample taker into the treatment chamber can be examined, forwarded and/or filled, or the sample taker can be checked, cleaned and/or replaced. If one or more media need to be added to the process, in the service position, the sample taker can be filled with medium by means of a corresponding apparatus and then moved by the retractable assembly into the process.
Especially in pharmaceutical technology, however, for example, also in the chemicals and foods industries, retractable assemblies are used to monitor the manufacturing of products. The monitored processes must be kept very clean, i.e. free of impurities, partially even sterile, since a contamination of the process media with impurities, or, generally, with undesired media, influences the end product, and, thus, also the customers, or, depending on application, also the patients.
The use of retractable assemblies in sterile processes is problematic, since washing, or rinsing, media, e.g. calibration liquids, lubricants of the drive or other impurities can be allowed in no case to reach the process, because thereby the product safety or the patient safety would be endangered, as well as customer satisfaction damaged.
It is questionable that, in the case of known solutions, there is no reliable isolation between the treatment chamber and the drive. As a result thereof, in the presence of a lack of sealing in the region of the treatment chamber, medium can migrate unnoticed into the drive, which can lead to a failure of the drive;, moreover, it is not out of the question that medium can escape via the drive unit into the environment. Worse, however, is, that “unclean”, certainly, however, unsterile materials can migrate or be dragged from the drive chamber or the environment into the treatment chamber and, thus, in the “clean”, possibly even sterile, region of the retractable assembly. In the most unfavorable case, the unclean materials get from the treatment chamber into the process. Then, the medium becomes contaminated with undesired materials and cannot be used for patients or customers. Critical characterizing adjectives for the medium can include, for example: Valuable, expensive, combustible, etching or corrosive, poisonous, bio-endangering, radioactive, etc.